It is well known to collect dust particles and other particulate material in containers or the like for later disposal or use. The containers may be provided with an air filter system. The material may be supplied to the containers by means of a gaseous flow through a ducting. The dust may be explosive. In some situations, an ignition may occur in the container due to ignition sources transported to the container with the airflow or due to ignition sources inside the container. Such ignition may result in devastating effects both on personnel, buildings, and the equipment, since the ignition may cause an explosion with a pressure wave and a flame front which travels back along the ducting opposite to the normal airflow direction.
In order of preventing such pressure wave and a flame front from travelling back along the ducting, it is well known to provide a back pressure flap valve arrangement in the ducting. The back pressure flap valve arrangement typically comprises a flap which is arranged to act as a check valve which may close off the ducting. During normal operation the flap is maintained in an open position by the dust or particle laden air stream flowing along the ducting. In the occasion of sudden pressure wave resulting from an upstream explosion, the flap is arranged to close the passage through the ducting by the pressure wave acting on the flap.
To avoid any rebound of the flap it is known to use a locking mechanism. One such locking mechanism is known from DE 202009011668U1. The document discloses a housing comprising a flap that is pivotably hinged around a shaft. The shaft is hinged in the walls of the housing and is further connected to a lever arranged on the exterior of the housing. The free end of the lever is arranged to slide along a sliding surface of a locking means to accommodate pivotal movements of the flap which occur during normal operation. Should the pivoting exceed a certain angle, the free end of the lever will engage a hook in the locking means and thereby lock the flap. The locking may be manually released by releasing the engagement between the lever and the locking means.
Lately, new regulations call for solutions where the valve stays closed long enough to avoid flames from transmitting during an explosion event. A new European standard is under preparation (FprEN 16447, Title: Explosion isolation flap valves). According to the proposed standard, the parts making up the flap valve should be constructed such that it can withstand the loads imposed by any explosion that can be expected in accordance with its intended use without loosing its ability to perform its safety function.